Field of the Invention
Embodiments of the present invention relate generally to a method of measuring beam positions of multi charged particle beams, and a multi charged particle beam writing apparatus, and more specifically, for example, relate to a method of measuring a beam position in multi beam writing.
Description of Related Art
In recent years, with high integration of LSI, the line width (critical dimension) of circuits of semiconductor devices is becoming progressively narrower. As a method for forming an exposure mask (also called a reticle) used to form circuit patterns on these semiconductor devices, the electron beam (EB) writing technique having excellent resolution is employed.
As an example employing the electron beam writing technique, a writing apparatus using multi-beams can be cited. Compared with the case of writing a pattern by using a single electron beam, since it is possible to emit multiple beams at a time (one shot) in multi-beam writing, the throughput can be greatly increased. For example, in a writing apparatus employing a multi-beam system, multi-beams are formed by making portions of an electron beam emitted from an electron gun pass through a corresponding hole of a plurality of holes formed in the mask, blanking control is performed for each beam, and each unblocked beam is reduced by an optical system and deflected by a deflector so as to irradiate a desired position on a target object or “sample”.
Now, regarding the beam position, since the beam position of multi-beams directly affects writing dimensions, it is important to accurately know the beam positions of multi-beams in order to maintain the dimensional accuracy of multi-beam writing. However, since the amount of current per beam used for multi-beam writing is small and its signal strength is weak, there is a problem in that the measurement accuracy decreases in measuring each beam, and therefore it is difficult to highly accurately measure beam positions of multi-beams. Accordingly, in the method described above, it has been difficult to correctly and accurately know beam positions of multi-beams. Moreover, since the number of beams configuring multi-beams is very large, there is also a problem in that it takes a long time to measure positions of all the multi-beams.
Regarding the multi-beam technique, there is disclosed a technique in which, when measuring a deflection sensitivity of main-sub two-stage deflection, positions are measured by scanning marks having a periodic structure with a beam pitch, by using beamlets configured by a plurality of beams (e.g., refer to Japanese Patent Application Laid-open (JP-A) No. 2006-245096).